My tire light is on and I do not know which one or if all the valves are defective. How do I find out?

If you have already tried putting air in tires and light is still on you will have to take to tire store they have a tool that can tell you which sensor is bad and tire will have to be removed from rim to replace sensor.

Yea I tried checking the inflation without success. I will check the shop. Thanks

I remember the good old days when we carried a simple gauge, and checked once or twice a month. Or if a tire looked low. Matter of fact I still do. My Corolla does not have TPMS and if it did I would get rid of it, instead of depending on electronic devices that give us trouble .... Just my opinion..... and don't forget the spare.. it has a monitor too. The donut should be 50 or 60 psi, I don't remember without going out to car, but look on the tire. It's embossed on it

Definitely agree with David my tire light is on now but not going to replace sensor because I keep a check on the air pressure in my tires just hope it will burn out one day.

Yup. A mechanical gauge over a radio transmitter any day